Not certainly; there are some scenarios which you wouldn't be able to plan. These scenarios usually knock only once and happen in very short time; it can be considered as jockpot for a trader. A plan is just a guide, thus it won't decide your winnings.
but still it can reduce the risk compared to trading without a plan. we know that before trading, gathering useful information is very necessary, and making restrictions so that we avoid the risk of loss. when you don't make a plan, of course you will only hold back and wait for the price to return to normal, when the price has fallen.